This invention relates to the art of packaging machinery and more particularly to that class of overwrapping machine known generally as L-sealers and particularly to the type of in-line L-sealer disclosed in Shanklin U.S. Pat. No. 3,583,888.
There are certain types of packages which can be overwrapped readily in manual and semi-automatic machines which are not suitable for use in the existing types of automatic L-sealers. These include, for example, reams of paper, stacks of books, stacks of carpet tile, boxed cakes and other bakery products, trays of cookies and the like. The reason for this is several-fold.
One is that to obtain good performance during the shrinking step and a good appearance in the final overwrap wrapped and shrunk package it is desirable that the seal approximately intersect the fold line in the pre-folded film and that the combined fold and seal line about the package be approximately at the mid-point of the height of the package. In practice this means that in the conventional L-sealer the level of the base of the sealing area on which the package rests during the sealing operation be below the level of the tray in the package insertion area by approximately one-half of the height of the package.
Secondly, in existing in-line automatic L-sealers, the package is advanced across the package insertion area by means of a reciprocating pusher arm which requires that the infeed conveyor or station be elevated above the insertion tray by a distance at least equal to the height of the pusher arm so that the package may pass over the pusher arm on being advanced from the infeed station to the insertion station.
In addition, since the package insertion arm merely reciprocates the arm has to go through a full stroke and return to its initial position before the next package can be transferred from the infeed station to the insertion station. This means that the motion of the reciprocating arm while the package is being advanced must be relatively rapid and hence violent, if it is desired to operate an automatic L-sealer at a reasonable speed. In addition, since the infeed conveyor cannot be started to feed the next package during the return stroke of the insertion arm, the speed of the conveyor must be rapid resulting in violent starts and stops of the product. The combination of the sudden drops and the rapid motion of the reciprocating arm and infeed conveyor tend to make existing automatic L-sealers unsuitable for items which can be damaged or dislodged by sudden movement and shock such as those mentioned above.